Independent oil refiners Delek US Partners (DK) and Alon USA (ALJ) boosted margins as they took advantage of cheaper shale oil coming out of Midland, Texas. "The positive margin environment that we saw during most of 2012 continued to remain strong through the fourth quarter," Alon CEO Paul Eisman said in a statement. Both firms said they were able to feed their inland refineries with more West Texas Intermediary crude, from Midland, Texas, which